/*
 fatfile.c

 Functions used by the newlib disc stubs to interface with
 this library

 Copyright (c) 2006 Michael "Chishm" Chisholm

 Redistribution and use in source and binary forms, with or without modification,
 are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice,
     this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice,
     this list of conditions and the following disclaimer in the documentation and/or
     other materials provided with the distribution.
  3. The name of the author may not be used to endorse or promote products derived
     from this software without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE
 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  2006-07-11 - Chishm
    * Original release

  2006-07-17 - Chishm
    * Made all path inputs const char*
    * Added _FAT_rename_r

  2006-08-02 - Chishm
    * Fixed _FAT_seek_r

  2006-08-13 - Chishm
    * Moved all externally visible directory related functions to fatdir
*/


#include "fatfile.h"

#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <unistd.h>

#include "cache.h"
#include "file_allocation_table.h"
#include "bit_ops.h"
#include "filetime.h"

/*static void _FAT_file_resetPosition (FILE_STRUCT* file) {
  PARTITION* partition = file->partition;

  file->currentPosition = 0;

  file->rwPosition.cluster = file->startCluster;
  file->rwPosition.sector = 0;
  file->rwPosition.byte = 0;

  file->appendPosition.cluster = _FAT_fat_lastCluster (partition, file->startCluster);
  file->appendPosition.sector = (file->filesize % partition->bytesPerCluster) / BYTES_PER_READ;
  file->appendPosition.byte = file->filesize % BYTES_PER_READ;
}*/

int _FAT_open_r (struct _reent *r, void *fileStruct, const char *path, int flags, int mode) {
  PARTITION* partition = NULL;
  bool fileExists;
  DIR_ENTRY dirEntry;
  const char* pathEnd;
  u32 dirCluster;
  FILE_STRUCT* file = (FILE_STRUCT*) fileStruct;
  partition = _FAT_partition_getPartitionFromPath (path);

  if (partition == NULL) {
    r->_errno = ENODEV;
    return -1;
  }

  // Move the path pointer to the start of the actual path
  if (strchr (path, ':') != NULL) {
    path = strchr (path, ':') + 1;
  }
  if (strchr (path, ':') != NULL) {
    r->_errno = EINVAL;
    return -1;
  }

  // Determine which mode the file is openned for
  if ((flags & 0x03) == O_RDONLY) {
    // Open the file for read-only access
    file->read = true;
    file->write = false;
    file->append = false;
  } else if ((flags & 0x03) == O_WRONLY) {
    // Open file for write only access
    file->read = false;
    file->write = true;
    file->append = false;
  } else if ((flags & 0x03) == O_RDWR) {
    // Open file for read/write access
    file->read = true;
    file->write = true;
    file->append = false;
  } else {
    r->_errno = EACCES;
    return -1;
  }

  // Make sure we aren't trying to write to a read-only disc
  if (file->write && partition->readOnly) {
    r->_errno = EROFS;
    return -1;
  }

  // Search for the file on the disc
  fileExists = _FAT_directory_entryFromPath (partition, &dirEntry, path, NULL);

  // The file shouldn't exist if we are trying to create it
  if ((flags & O_CREAT) && (flags & O_EXCL) && fileExists) {
    r->_errno = EEXIST;
    return -1;
  }

  // It should not be a directory if we're openning a file,
  if (fileExists && _FAT_directory_isDirectory(&dirEntry)) {
    r->_errno = EISDIR;
    return -1;
  }

  // If the file doesn't exist, create it if we're allowed to
  if (!fileExists) {
    if (flags & O_CREAT) {
      if (partition->readOnly) {
        // We can't write to a read-only partition
        r->_errno = EROFS;
        return -1;
      }
      // Create the file
      // Get the directory it has to go in
      pathEnd = strrchr (path, DIR_SEPARATOR);
      if (pathEnd == NULL) {
        // No path was specified
        dirCluster = partition->cwdCluster;
        pathEnd = path;
      } else {
        // Path was specified -- get the right dirCluster
        // Recycling dirEntry, since it needs to be recreated anyway
        if (!_FAT_directory_entryFromPath (partition, &dirEntry, path, pathEnd) ||
          !_FAT_directory_isDirectory(&dirEntry)) {
          r->_errno = ENOTDIR;
          return -1;
        }
        dirCluster = _FAT_directory_entryGetCluster (partition, dirEntry.entryData);
        // Move the pathEnd past the last DIR_SEPARATOR
        pathEnd += 1;
      }
      // Create the entry data
      strncpy (dirEntry.filename, pathEnd, MAX_FILENAME_LENGTH - 1);
      memset (dirEntry.entryData, 0, DIR_ENTRY_DATA_SIZE);

      // Set the creation time and date
      dirEntry.entryData[DIR_ENTRY_cTime_ms] = 0;
      u16_to_u8array (dirEntry.entryData, DIR_ENTRY_cTime, _FAT_filetime_getTimeFromRTC());
      u16_to_u8array (dirEntry.entryData, DIR_ENTRY_cDate, _FAT_filetime_getDateFromRTC());

      if (!_FAT_directory_addEntry (partition, &dirEntry, dirCluster)) {
        r->_errno = ENOSPC;
        return -1;
      }
    } else {
      // file doesn't exist, and we aren't creating it
      r->_errno = ENOENT;
      return -1;
    }
  }

  file->filesize = u8array_to_u32 (dirEntry.entryData, DIR_ENTRY_fileSize);

  /* Allow LARGEFILEs with undefined results
  // Make sure that the file size can fit in the available space
  if (!(flags & O_LARGEFILE) && (file->filesize >= (1<<31))) {
    r->_errno = EFBIG;
    return -1;
  }
  */

  // Make sure we aren't trying to write to a read-only file
  if (file->write && !_FAT_directory_isWritable(&dirEntry)) {
    r->_errno = EROFS;
    return -1;
  }

  // Associate this file with a particular partition
  file->partition = partition;

  file->startCluster = _FAT_directory_entryGetCluster (partition, dirEntry.entryData);

  // Truncate the file if requested
  if ((flags & O_TRUNC) && file->write && (file->startCluster != 0)) {
    _FAT_fat_clearLinks (partition, file->startCluster);
    file->startCluster = 0;
    file->filesize = 0;
  }

  // Remember the position of this file's directory entry
  file->dirEntryStart = dirEntry.dataStart;   // Points to the start of the LFN entries of a file, or the alias for no LFN
  file->dirEntryEnd = dirEntry.dataEnd;

  // Reset read/write pointer
  file->currentPosition = 0;
  file->rwPosition.cluster = file->startCluster;
  file->rwPosition.sector =  0;
  file->rwPosition.byte = 0;

  if (flags & O_APPEND) {
    file->append = true;

    // Set append pointer to the end of the file
    file->appendPosition.cluster = _FAT_fat_lastCluster (partition, file->startCluster);
    file->appendPosition.sector = (file->filesize % partition->bytesPerCluster) / BYTES_PER_READ;
    file->appendPosition.byte = file->filesize % BYTES_PER_READ;

    // Check if the end of the file is on the end of a cluster
    if ( (file->filesize > 0) && ((file->filesize % partition->bytesPerCluster)==0) ){
      // Set flag to allocate a new cluster
      file->appendPosition.sector = partition->sectorsPerCluster;
      file->appendPosition.byte = 0;
    }
  } else {
    file->append = false;
    // Use something sane for the append pointer, so the whole file struct contains known values
    file->appendPosition = file->rwPosition;
  }


  file->inUse = true;

  partition->openFileCount += 1;

  return (int) file;
}

int _FAT_close_r (struct _reent *r, int fd) {
  FILE_STRUCT* file = (FILE_STRUCT*)  fd;
  u8 dirEntryData[DIR_ENTRY_DATA_SIZE];

  if (!file->inUse) {
    r->_errno = EBADF;
    return -1;
  }
  if (file->write) {
    // Load the old entry
    _FAT_cache_readPartialSector (file->partition->cache, dirEntryData,
      _FAT_fat_clusterToSector(file->partition, file->dirEntryEnd.cluster) + file->dirEntryEnd.sector,
      file->dirEntryEnd.offset * DIR_ENTRY_DATA_SIZE, DIR_ENTRY_DATA_SIZE);

    // Write new data to the directory entry
    // File size
    u32_to_u8array (dirEntryData, DIR_ENTRY_fileSize, file->filesize);

    // Start cluster
    u16_to_u8array (dirEntryData, DIR_ENTRY_cluster, file->startCluster);
    u16_to_u8array (dirEntryData, DIR_ENTRY_clusterHigh, file->startCluster >> 16);

    // Modification time and date
    u16_to_u8array (dirEntryData, DIR_ENTRY_mTime, _FAT_filetime_getTimeFromRTC());
    u16_to_u8array (dirEntryData, DIR_ENTRY_mDate, _FAT_filetime_getDateFromRTC());

    // Access date
    u16_to_u8array (dirEntryData, DIR_ENTRY_aDate, _FAT_filetime_getDateFromRTC());

    // Write the new entry
    _FAT_cache_writePartialSector (file->partition->cache, dirEntryData,
      _FAT_fat_clusterToSector(file->partition, file->dirEntryEnd.cluster) + file->dirEntryEnd.sector,
      file->dirEntryEnd.offset * DIR_ENTRY_DATA_SIZE, DIR_ENTRY_DATA_SIZE);

    // Flush any sectors in the disc cache
    if (!_FAT_cache_flush(file->partition->cache)) {
      r->_errno = EIO;
      return -1;
    }
  }

  file->inUse = false;
  file->partition->openFileCount -= 1;

  return 0;
}

int _FAT_read_r (struct _reent *r, int fd, char *ptr, int len) {
  FILE_STRUCT* file = (FILE_STRUCT*)  fd;
  PARTITION* partition;
  CACHE* cache;

  FILE_POSITION position;
  u32 tempNextCluster;

  int tempVar;

  u32 remain;

  bool flagNoError = true;

  // Make sure we can actually read from the file
  if ((file == NULL) || !file->inUse || !file->read) {
    r->_errno = EBADF;
    return 0;
  }

  // Don't try to read if the read pointer is past the end of file
  if (file->currentPosition >= file->filesize || file->startCluster == CLUSTER_FREE) {
    r->_errno = EOVERFLOW;
    return 0;
  }

  // Don't read past end of file
  if (len + file->currentPosition > file->filesize) {
    r->_errno = EOVERFLOW;
    len = file->filesize - file->currentPosition;
  }
  
  // Short circuit cases where len is 0 (or less)
  if (len <= 0) {
    return 0;
  }

  remain = len;

  position = file->rwPosition;

  partition = file->partition;
  cache = file->partition->cache;

  // Align to sector
  tempVar = BYTES_PER_READ - position.byte;
  if (tempVar > remain) {
    tempVar = remain;
  }

  if ((tempVar < BYTES_PER_READ) && flagNoError)
  {
    _FAT_cache_readPartialSector ( cache, ptr, _FAT_fat_clusterToSector (partition, position.cluster) + position.sector,
      position.byte, tempVar);

    remain -= tempVar;
    ptr += tempVar;

    position.byte += tempVar;
    if (position.byte >= BYTES_PER_READ) {
      position.byte = 0;
      position.sector++;
    }
  }

  // align to cluster
  // tempVar is number of sectors to read
  if (remain > (partition->sectorsPerCluster - position.sector) * BYTES_PER_READ) {
    tempVar = partition->sectorsPerCluster - position.sector;
  } else {
    tempVar = remain / BYTES_PER_READ;
  }

  if ((tempVar > 0) && flagNoError) {
    if (! _FAT_disc_readSectors (partition->disc, _FAT_fat_clusterToSector (partition, position.cluster) + position.sector,
	  tempVar, ptr)) 
	{
	  flagNoError = false;
	  r->_errno = EIO;
	} else {
	  ptr += tempVar * BYTES_PER_READ;
	  remain -= tempVar * BYTES_PER_READ;
	  position.sector += tempVar;
	}
  }

  // Move onto next cluster
  // It should get to here without reading anything if a cluster is due to be allocated
  if (position.sector >= partition->sectorsPerCluster) {
    tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
    if ((remain == 0) && (tempNextCluster == CLUSTER_EOF)) {
      position.sector = partition->sectorsPerCluster;
    } else if (tempNextCluster == CLUSTER_FREE) {
      r->_errno = EIO;
      flagNoError = false;
    } else {
      position.sector = 0;
      position.cluster = tempNextCluster;
    }
  }

  // Read in whole clusters, contiguous blocks at a time
	while ((remain >= partition->bytesPerCluster) && flagNoError) {
		uint32_t chunkEnd;
		uint32_t nextChunkStart = position.cluster;
		size_t chunkSize = 0;
	
		do {
			chunkEnd = nextChunkStart;
			nextChunkStart = _FAT_fat_nextCluster (partition, chunkEnd);
			chunkSize += partition->bytesPerCluster;
		} while ((nextChunkStart == chunkEnd + 1) && 
#ifdef LIMIT_SECTORS
		 	(chunkSize + partition->bytesPerCluster <= LIMIT_SECTORS * BYTES_PER_READ) && 
#endif
			(chunkSize + partition->bytesPerCluster <= remain));
		
		if (!_FAT_disc_readSectors (partition->disc, _FAT_fat_clusterToSector (partition, position.cluster),
				chunkSize / BYTES_PER_READ, ptr)) 
		{
			flagNoError = false;
			r->_errno = EIO;
			break;
		}
		ptr += chunkSize;
		remain -= chunkSize;

		// Advance to next cluster
		if ((remain == 0) && (nextChunkStart == CLUSTER_EOF)) {
			position.sector = partition->sectorsPerCluster;
			position.cluster = chunkEnd;
		} else if (!_FAT_fat_isValidCluster(partition, nextChunkStart)) {
			r->_errno = EIO;
			flagNoError = false;
		} else {
			position.sector = 0;
			position.cluster = nextChunkStart;
		}
	}

  // Read remaining sectors
  tempVar = remain / BYTES_PER_READ; // Number of sectors left
  if ((tempVar > 0) && flagNoError) {
    if (! _FAT_disc_readSectors (partition->disc, _FAT_fat_clusterToSector (partition, position.cluster),
	  tempVar, ptr)) 
	{
	  flagNoError = false;
	  r->_errno = EIO;
	} else {
	  ptr += tempVar * BYTES_PER_READ;
	  remain -= tempVar * BYTES_PER_READ;
	  position.sector += tempVar;
	}
  }

  // Last remaining sector
  // Check if anything is left
  if ((remain > 0) && flagNoError) {
    _FAT_cache_readPartialSector ( cache, ptr,
      _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
    position.byte += remain;
    remain = 0;
  }

  // Length read is the wanted length minus the stuff not read
  len = len - remain;

  // Update file information
  file->rwPosition = position;
  file->currentPosition += len;
  return len;
}

/*
Extend a file so that the size is the same as the rwPosition
*/
static bool file_extend_r (struct _reent *r, FILE_STRUCT* file) {
  PARTITION* partition = file->partition;
  CACHE* cache = file->partition->cache;

  FILE_POSITION position;

  u32 remain;

  u8 zeroBuffer [BYTES_PER_READ] = {0};

  u32 tempNextCluster;

  position.byte = file->filesize % BYTES_PER_READ;
  position.sector = (file->filesize % partition->bytesPerCluster) / BYTES_PER_READ;
  position.cluster = _FAT_fat_lastCluster (partition, file->startCluster);

  remain = file->currentPosition - file->filesize;
  
  if ((remain > 0) && (file->filesize > 0) && (position.sector == 0) && (position.byte  == 0)) {
    // Get a new cluster on the edge of a cluster boundary
    tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
    if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
      // Couldn't get a cluster, so abort
      r->_errno = ENOSPC;
      return false;
    } 
    position.cluster = tempNextCluster;
    position.sector = 0;
  }


  // Only need to clear to the end of the sector
  if (remain + position.byte < BYTES_PER_READ) {
    _FAT_cache_writePartialSector (cache, zeroBuffer,
      _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte, remain);
    position.byte += remain;
  } else {
    if (position.byte > 0) {
      _FAT_cache_writePartialSector (cache, zeroBuffer,
        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte,
        BYTES_PER_READ - position.byte);
      remain -= (BYTES_PER_READ - position.byte);
      position.byte = 0;
      position.sector ++;
    }

    while (remain >= BYTES_PER_READ) {
      if (position.sector >= partition->sectorsPerCluster) {
        position.sector = 0;
        // Ran out of clusters so get a new one
		tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
        if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
		  // Couldn't get a cluster, so abort
		  r->_errno = ENOSPC;
		  return false;
		}
		position.cluster = tempNextCluster;
      }

      _FAT_disc_writeSectors (partition->disc,
        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 1, zeroBuffer);

      remain -= BYTES_PER_READ;
      position.sector ++;
    }

    if (position.sector >= partition->sectorsPerCluster) {
      position.sector = 0;
      tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
      if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
        // Ran out of clusters so get a new one
        tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
      }
      if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
        // Couldn't get a cluster, so abort
        r->_errno = ENOSPC;
        return false;
      } else {
        position.cluster = tempNextCluster;
      }
    }

    if (remain > 0) {
      _FAT_cache_writePartialSector (cache, zeroBuffer,
        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
      position.byte = remain;
    }
  }

  file->rwPosition = position;
  file->filesize = file->currentPosition;
  return true;
}


int _FAT_write_r (struct _reent *r,int fd, const char *ptr, int len) {
  FILE_STRUCT* file = (FILE_STRUCT*)  fd;

  PARTITION* partition;
  CACHE* cache;

  FILE_POSITION position;
  u32 tempNextCluster;

  int tempVar;

  u32 remain;

  bool flagNoError = true;
  bool flagAppending = false;

  // Make sure we can actually write to the file
  if ((file == NULL) || !file->inUse || !file->write) {
    r->_errno = EBADF;
    return -1;
  }

  partition = file->partition;
  cache = file->partition->cache;
  
  // Only write up to the maximum file size, taking into account wrap-around of ints
  if (remain + file->filesize > FILE_MAX_SIZE || len + file->filesize < file->filesize) {
    len = FILE_MAX_SIZE - file->filesize;	
  }
	
  remain = len;
  
  // Short circuit cases where len is 0 (or less)
  if (len <= 0) {
    return 0;
  }

  // Get a new cluster for the file if required
  if (file->startCluster == CLUSTER_FREE) {
    tempNextCluster = _FAT_fat_linkFreeCluster (partition, CLUSTER_FREE);
	if (!_FAT_fat_isValidCluster(partition, tempNextCluster)) {
	  // Couldn't get a cluster, so abort immediately
	  r->_errno = ENOSPC;
	  return -1;
	}
	
	file->startCluster = tempNextCluster;
		
    // Appending starts at the begining for a 0 byte file
	file->appendPosition.cluster = file->startCluster;
	file->appendPosition.sector = 0;
	file->appendPosition.byte = 0;

	file->rwPosition.cluster = file->startCluster;
	file->rwPosition.sector =  0;
	file->rwPosition.byte = 0;
  }

  if (file->append) {
    position = file->appendPosition;
    flagAppending = true;
  } else {
    // If the write pointer is past the end of the file, extend the file to that size
    if (file->currentPosition > file->filesize) {
      if (!file_extend_r (r, file)) {
        return 0;
      }
    }

    // Write at current read pointer
    position = file->rwPosition;

    // If it is writing past the current end of file, set appending flag
    if (len + file->currentPosition > file->filesize) {
      flagAppending = true;
    }
  }

  // Move onto next cluster if needed
  if (position.sector >= partition->sectorsPerCluster) {
    position.sector = 0;
    tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
    if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
      // Ran out of clusters so get a new one
      tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
    }
    if (tempNextCluster == CLUSTER_FREE) {
      // Couldn't get a cluster, so abort
      r->_errno = ENOSPC;
      flagNoError = false;
    } else {
      position.cluster = tempNextCluster;
    }
  }

  // Align to sector
  tempVar = BYTES_PER_READ - position.byte;
  if (tempVar > remain) {
    tempVar = remain;
  }

  if ((tempVar < BYTES_PER_READ) && flagNoError) {
    // Write partial sector to disk
    _FAT_cache_writePartialSector (cache, ptr,
      _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, position.byte, tempVar);

    remain -= tempVar;
    ptr += tempVar;
    position.byte += tempVar;


    // Move onto next sector
    if (position.byte >= BYTES_PER_READ) {
      position.byte = 0;
      position.sector ++;
    }
  }

  // Align to cluster
  // tempVar is number of sectors to write
  if (remain > (partition->sectorsPerCluster - position.sector) * BYTES_PER_READ) {
    tempVar = partition->sectorsPerCluster - position.sector;
  } else {
    tempVar = remain / BYTES_PER_READ;
  }

  if ((tempVar > 0) && flagNoError) {
    if (!_FAT_disc_writeSectors (partition->disc, 
	  _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, tempVar, ptr))
	{
	  flagNoError = false;
	  r->_errno = EIO;
	} else {
	  ptr += tempVar * BYTES_PER_READ;
	  remain -= tempVar * BYTES_PER_READ;
	  position.sector += tempVar;
	}
  }

  if ((position.sector >= partition->sectorsPerCluster) && flagNoError && (remain > 0)) {
    position.sector = 0;
    tempNextCluster = _FAT_fat_nextCluster(partition, position.cluster);
    if ((tempNextCluster == CLUSTER_EOF) || (tempNextCluster == CLUSTER_FREE)) {
      // Ran out of clusters so get a new one
      tempNextCluster = _FAT_fat_linkFreeCluster(partition, position.cluster);
    }
    if (tempNextCluster == CLUSTER_FREE) {
      // Couldn't get a cluster, so abort
      r->_errno = ENOSPC;
      flagNoError = false;
    } else {
      position.cluster = tempNextCluster;
    }
  }

  	// Write whole clusters, contiguous blocks at a time
	while ((remain >= partition->bytesPerCluster) && flagNoError) {
		uint32_t chunkEnd;
		uint32_t nextChunkStart = position.cluster;
		size_t chunkSize = 0;
	
		do {
			chunkEnd = nextChunkStart;
			nextChunkStart = _FAT_fat_nextCluster (partition, chunkEnd);
			if ((nextChunkStart == CLUSTER_EOF) || (nextChunkStart == CLUSTER_FREE)) {
				// Ran out of clusters so get a new one
				nextChunkStart = _FAT_fat_linkFreeCluster(partition, chunkEnd);
			} 
			if (!_FAT_fat_isValidCluster(partition, nextChunkStart)) {
				// Couldn't get a cluster, so abort
				r->_errno = ENOSPC;
				flagNoError = false;
			} else {
				chunkSize += partition->bytesPerCluster;
			}
		} while (flagNoError && (nextChunkStart == chunkEnd + 1) && 
#ifdef LIMIT_SECTORS
		 	(chunkSize + partition->bytesPerCluster <= LIMIT_SECTORS * BYTES_PER_READ) && 
#endif
			(chunkSize + partition->bytesPerCluster <= remain));

		if ( !_FAT_disc_writeSectors (partition->disc, _FAT_fat_clusterToSector(partition, position.cluster),
			chunkSize / BYTES_PER_READ, ptr)) 
		{
			flagNoError = false;
			r->_errno = EIO;
			break;
		}
		ptr += chunkSize;
		remain -= chunkSize;
		
		if (_FAT_fat_isValidCluster(partition, nextChunkStart)) {
			position.cluster = nextChunkStart;
		} else {
			// Allocate a new cluster when next writing the file
			position.cluster = chunkEnd;
			position.sector = partition->sectorsPerCluster;
		}
	}

  // Write remaining sectors
  tempVar = remain / BYTES_PER_READ; // Number of sectors left
  if ((tempVar > 0) && flagNoError) {
    if (!_FAT_disc_writeSectors (partition->disc, _FAT_fat_clusterToSector (partition, position.cluster), 
	  tempVar, ptr))
	{
	  flagNoError = false;
	  r->_errno = EIO;
	} else {
	  ptr += tempVar * BYTES_PER_READ;
	  remain -= tempVar * BYTES_PER_READ;
	  position.sector += tempVar;
	}
  }

  // Last remaining sector
  if ((remain > 0) && flagNoError) {
    if (flagAppending) {
      _FAT_cache_eraseWritePartialSector ( cache, ptr,
        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
    } else {
      _FAT_cache_writePartialSector ( cache, ptr,
        _FAT_fat_clusterToSector (partition, position.cluster) + position.sector, 0, remain);
    }
    position.byte += remain;
    remain = 0;
  }


  // Amount read is the originally requested amount minus stuff remaining
  len = len - remain;

  // Update file information
  if (file->append) {
    // Appending doesn't affect the read pointer
    file->appendPosition = position;
    file->filesize += len;
  } else {
    // Writing also shifts the read pointer
    file->rwPosition = position;
    file->currentPosition += len;
    if (file->filesize < file->currentPosition) {
      file->filesize = file->currentPosition;
    }
  }

  return len;
}


int _FAT_seek_r (struct _reent *r, int fd, int pos, int dir) {
  FILE_STRUCT* file = (FILE_STRUCT*)  fd;

  PARTITION* partition;

  u32 cluster, nextCluster;
  int clusCount;
  uint32_t position;
  off_t newPosition;

  if ((file == NULL) || (file->inUse == false))  {
    // invalid file
    r->_errno = EBADF;
    return -1;
  }

  partition = file->partition;

  switch (dir) {
    case SEEK_SET:
      newPosition = pos;
      break;
    case SEEK_CUR:
      newPosition = file->currentPosition + pos;
      break;
    case SEEK_END:
      newPosition = file->filesize + pos;
      break;
    default:
      r->_errno = EINVAL;
      return -1;
  }

  if ((pos > 0) && (position < 0)) {
    r->_errno = EOVERFLOW;
    return -1;
  }
  
  // newPosition can only be larger than the FILE_MAX_SIZE on platforms where 
  // off_t is larger than 32 bits.
  if (newPosition < 0 || ((sizeof(newPosition) > 4) && newPosition > (off_t)FILE_MAX_SIZE)) {
    r->_errno = EINVAL;
    return -1;
  }
  
  position = (uint32_t)newPosition;

  // Only change the read/write position if it is within the bounds of the current filesize,
  // or at the very edge of the file
  if (position <= file->filesize && file->startCluster != CLUSTER_FREE) {

    // Calculate the sector and byte of the current position,
    // and store them
    file->rwPosition.sector = (position % partition->bytesPerCluster) / BYTES_PER_READ;
    file->rwPosition.byte = position % BYTES_PER_READ;

    // Calculate where the correct cluster is
    if (position >= file->currentPosition) {
      clusCount = (position / partition->bytesPerCluster) - (file->currentPosition / partition->bytesPerCluster);
      cluster = file->rwPosition.cluster;
    } else {
      clusCount = position / partition->bytesPerCluster;
      cluster = file->startCluster;
    }

    nextCluster = _FAT_fat_nextCluster (partition, cluster);
    while ((clusCount > 0) && (nextCluster != CLUSTER_FREE) && (nextCluster != CLUSTER_EOF)) {
      clusCount--;
      cluster = nextCluster;
      nextCluster = _FAT_fat_nextCluster (partition, cluster);
    }

    // Check if ran out of clusters, and the file is being written to
	if (clusCount > 0) {
	  if ((clusCount == 1) && (file->filesize == position) && (file->rwPosition.sector == 0)) {
	    // Set flag to allocate a new cluster
	    file->rwPosition.sector = partition->sectorsPerCluster;
	    file->rwPosition.byte = 0;
	  } else {
	    r->_errno = EINVAL;
	    return -1;
	  }
	}

    file->rwPosition.cluster = cluster;
  }

  // Save position
  file->currentPosition = position;

  return position;
}



int _FAT_fstat_r (struct _reent *r, int fd, struct stat *st) {
  FILE_STRUCT* file = (FILE_STRUCT*)  fd;

  PARTITION* partition;

  DIR_ENTRY fileEntry;

  if ((file == NULL) || (file->inUse == false))  {
    // invalid file 
    r->_errno = EBADF;
    return -1;
  }

  partition = file->partition;

  // Get the file's entry data
  fileEntry.dataStart = file->dirEntryStart;
  fileEntry.dataEnd = file->dirEntryEnd;

  if (!_FAT_directory_entryFromPosition (partition, &fileEntry)) {
    r->_errno = EIO;
    return -1;
  }

  // Fill in the stat struct
  _FAT_directory_entryStat (partition, &fileEntry, st);

  // Fix stats that have changed since the file was openned
    st->st_ino = (ino_t)(file->startCluster);   // The file serial number is the start cluster
  st->st_size = file->filesize;         // File size

  return 0;
}
